1. Field of the Invention
The present invention relates to an apparatus and method of filling a mold for manufacturing an ophthalmic lens.
2. Background Art
Most lenses today are made by molding plastic because of its light weight, density, refractive index, and impact resistance. To form a lens, two molding shells, often referred as a front mold and a back mold in the art of lens making, are used. Each molding shell has a facing inside surface. When these two molding shells are properly positioned at a desired distance and rotational orientation to each other, their facing inside surfaces are a negative image of the surfaces of the lens to be formed. A closure member is used to cooperate with the molding shells to form a mold with a molding cavity. Then a fluid lens-forming material, normally a liquid monomer, is inserted into and contained in the molding cavity defined by the two molding shells and the closure member. The closure member normally has a casting opening through which the fluid lens-forming material is introduced into the cavity. Once the fluid lens-forming material is in the cavity, it is cured to form a hardened polymeric lens taking the shape of the molds.
Currently, there are two ways to fill a mold in molding the lenses in the art. The first, conventional way is a xe2x80x9ctopxe2x80x9d filling method as shown in FIG. 1 of this specification. In FIG. 1, a mold M with a molding cavity C is vertically positioned so that an opening V is at the top of the mold M. A filling device (not shown) in connection with a reservoir of a fluid lens-forming material delivers the fluid lens-forming material into the molding cavity C through a filling needle via the opening V. The opening V also functions as an air venting channel during the process. Inevitably, some air bubbles B generated during the filling process may be easily trapped at the opening V and may form an air block that slows down the filling process. Moreover, the xe2x80x9csyrupxe2x80x9deffect well known to glass makers is also evident with this xe2x80x9ctopxe2x80x9d filling method. That is, given the viscosity of the lens-forming material, the fluid flows slowly, in xe2x80x9cruns,xe2x80x9d into the molding cavity C and the air block formed at the opening V further frustrates the filling process. Because of the uneven, slow flow of the fluid lens-forming material into the molding cavity C, the likelihood of optical defects in the resulting lens is increased.
The second filling method is a xe2x80x9cbottomxe2x80x9d filling method as shown in FIG. 2 of this specification. In FIG. 2, a casting opening O is separated from the venting opening V in about 180xc2x0. The mold M is positioned so that the casting opening O is located at the bottom of the mold M. The lens-forming material is introduced into the molding cavity C from the bottom through the casting opening O. To overcome gravity, pumping means (not shown) may be used to cause the lens-forming material to flow into the cavity C without significantly pressurizing it. Air venting is provided through the venting opening V located at the top of the molding cavity C. Because this filling method separates the venting opening from the casting opening, the interference of air bubbles with the flow of the fluid lens-forming material is eliminated and the xe2x80x9csyrupxe2x80x9d effect is reduced greatly. Thus, it is able to shorten the filling process significantly.
However, the bottom filling method introduces a potential new quality problem. As known to the people skilled in the art, the center region of a formed optical lens is the most optically active area. Therefore, any defect in this region will compromise the quality of the formed lens. Because air bubbles inevitably produce optical defects, it is preferred not to allow the air bubbles to pass through this optically active region. However, as shown in FIG. 2, the air bubbles B have to travel through the most optically active region to reach the venting opening V. In fact, the air bubbles B cross the entire molding cavity C, which significantly increases the likelihood of optical defects in the finished lens. Thus, the bottom filling method may seriously compromise the optical quality of the formed optical lens.
Accordingly, there exists a need for an improved apparatus and method for filling a mold for molding optical lenses.
The present invention overcomes the disadvantages of the prior art and discloses an entirely new method of filling a mold for molding lens and related apparatus. In one aspect, the present invention relates to a method for molding an optical lens. In one embodiment, the method includes the steps of providing a mold having two molding shells disposed on edge and substantially vertically oriented, and an annular closure member having an outer surface disposed at the periphery of the molding shells cooperating with the two molding shells to define a molding cavity having a center, a vertical axis and a horizontal axis perpendicular thereto, both axes passing through the center to thereby divide the mold into an upper portion and a lower portion, a venting opening and a casting port disposed at the upper portion of the mold and spaced apart from each other at an acute angle, wherein the venting opening is in fluid communication with the ambient air and the molding cavity, and the casting port is separated from the ambient air by the outer surface of the closure member and in fluid communication with the molding cavity, introducing a fluid lens-forming material into the molding cavity through the casting port, curing the fluid lens-forming material so that the fluid lens-forming material is hardened to form the optical lens, and removing the optical lens from the molding cavity.
Because of the separation and the special geometric arrangement of the venting opening and the casting port, the fluid lens-forming material is filled into the molding cavity without interference from the air venting process. Any trapped air bubbles travel to the venting opening and out of the mold from there due to gravity without passing through the optically active area of the optical lens formed. Moreover, the filling of the fluid lens-forming material is further facilitated by gravity and a pumping device is no longer necessary. Thus, the present invention avoids the xe2x80x9csyrupxe2x80x9d effect, improves the quality of the lens formed and further facilitates the filling process.
In another aspect, the present invention relates to a method for molding an optical lens. In one embodiment, the method includes the steps of providing a mold having two molding shells disposed on edge and substantially vertically oriented, and an annular closure member disposed at the periphery cooperating with the two molding shells to define a molding cavity which has a center, a vertical axis and a horizontal axis perpendicular to each other, both axes passing through the center to thereby divide the mold into an upper portion and a lower portion, a venting opening disposed at the upper portion of the mold and communicating with the molding cavity, injecting a fluid lens-forming material into the molding cavity through a port at a position at the upper portion of the mold but apart from the location of the venting opening at acute angle, wherein the port is separated from the ambient air by the outer surface of the closure member, curing the fluid lens-forming material so that the fluid lens-forming material is hardened to form the optical lens, and removing the optical lens from the molding cavity.
In a further aspect, the present invention relates to a method for molding an optical lens. In one embodiment, the method includes the steps of providing a mold having two molding shells disposed on edge and substantially vertically oriented, and an annular closure member having an outer surface disposed at the periphery cooperating with the two molding shells defining a molding cavity with a center and having a vertical axis and a horizontal axis perpendicular to each other, both axes passing through the center thereby dividing the mold into an upper portion and a lower portion, a venting opening and a plurality of casting openings disposed at the upper portion of the mold and spaced apart from each other, the venting opening and each of the casting openings forming an acute angle between them, the venting opening and the plurality of casting openings communicating with the molding cavity, wherein at least one of the plurality of casting openings is a port being separated from the ambient air by the outer surface of the closure member, introducing a fluid lens-forming material into the molding cavity through a casting opening, curing the fluid lens-forming material so that the fluid lens-forming material is hardened to form the optical lens, and removing the optical lens from the molding cavity.
In yet another aspect, the present invention relates to an apparatus for molding an optical lens. In one embodiment, the apparatus includes a front mold, a back mold, and a closure member having an outer surface and cooperating with the front mold and the back mold to form a molding cavity therebetween for molding the optical lens. The closure member has at least one venting opening and at least one casting port spaced apart from each other at an acute angle at an upper portion of the molding cavity, the venting opening being in fluid communication with the molding cavity and the ambient air and the casting port being in fluid communication with the molding cavity and separated from the ambient air by the outer surface of the closure member.
In yet a further aspect, the present invention relates to an improvement in an apparatus for molding an optical lens. The apparatus includes a pair of opposed molding shells disposed on edge and substantially vertically oriented and which form a molding cavity therebetween with a closure member having an outer surface, the molding cavity having a center, a vertical axis and a horizontal axis perpendicular to each other, a casting port being separated from the ambient air and communicating with the cavity for the introduction therethrough into the cavity a fluid lens-forming material and a venting opening communicating into the cavity. In one embodiment, the improvement includes the venting opening being disposed at the upper most point of the molding cavity, where the vertical axis intersects the closure member, the venting opening and the casting port forming an acute angle therebetween at an upper portion of the molding cavity.
In another aspect, the present invention relates to an apparatus for molding an optical lens. In one embodiment, the apparatus includes a front mold, a back mold, and a closure member having an inner surface and an outer surface and cooperating with the front mold and the back mold to form a molding cavity therebetween for molding the optical lens. The closure member has at least one venting opening and at least one casting port spaced apart from each other at an acute angle at an upper portion of the molding cavity, the venting opening and the casting port being connected by a recess channel located at the inner surface.
In all of the embodiments above, the closure member can be in the form of a gasket or a sleeve. For the latter, the sleeve can be formed from an elastomeric material. Thus, a filling needle can be used to pierce the elastomeric sleeve and then inject the fluid lens-forming mixture into the molding cavity.
The venting opening and casting opening can be pre-manufactured, or they may be formed during the filling process by, say, a filling needle. The sizes of the venting opening and the casting opening may be same or may be different.
In a further aspect, the present invention relates to a strip for molding an optical lens in cooperation with a front mold and a back mold. In one embodiment, the strip includes a body having a first end, a second end, and an inner surface and an opposed outer surface, and a recess channel formed on the inner surface. The recess channel can be formed on the inner surface continuously, extending from the first end to the second end of the body. Alternatively, the recess channel can be formed on the inner surface discontinuously. In use, the strip can be wrapped around the edges of the front mold and the back mold to form a sleeve cooperating with the front mold and the back mold to define a molding cavity.
In yet another aspect, the present invention relates to a sleeve for molding an optical lens in cooperation with a front mold and a back mold. In one embodiment, the sleeve includes a body portion having a first end and a second end, an inner surface and an opposed outer surface, a bore extending from the first end and the second end axially, a venting port formed on the body portion, a casting port formed on the body portion and positioned apart from the venting port, and a recess channel formed on the inner surface connecting the venting port and the casting port. The recess channel can be formed to extend continuously from the venting port and the casting port. The bore is adapted to receive the front mold and the back mold to define a molding cavity. Additionally, the casting port is formed intermediate the outer surface of the body portion and the bore such that the casting port is separated from the ambient air by the outer surface of the body portion and is in fluid communication with the molding cavity.
These and other aspects will become apparent from the following description of various embodiments taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.